The invention relates to a liquid chromatograph, more particularly, to a liquid chromatograph, which may be applied to a micro liquid chromatography wherein a mobile phase is delivered at a low flow rate in the order of, for example, 1-5 micro-liters/minute.
The micro liquid chromatography is used in a liquid chromatograph/mass spectrometer (LC/MS) and an analysis of a micro sample of protein or peptide, an absolute quantity of which is limited.
As a liquid delivery mechanism of a liquid chromatograph, there has been proposed a plunger reciprocating type liquid delivery pump for delivering a mobile phase through a reciprocating movement of a plunger. In the plunger reciprocating type liquid delivery pump, the plunger is reciprocated in a pump head by using a mechanism for converting a rotating movement of a driving motor into a linear movement. The mobile phase is sucked into the pump head by the reciprocating movement of the plunger and actions of a check valve or a flow line selecting valve provided on a liquid entrance side and a liquid exit side of the pump head, respectively, and then is discharged to a column side from a sample injection portion.
As the plunger reciprocating type liquid delivery pump as described above, there have been proposed a single plunger type pump formed of one set of the plunger and the pump head, and a double plunger type pump including two sets of the plungers and pump heads disposed in parallel or in series.
In the plunger reciprocating type liquid delivery pump, a liquid is delivered by repeating discharging and sucking operations by reciprocating the plunger. An operation cycle of a liquid delivery pump to be used in a normal liquid chromatograph is independent, not in synchronism with an analyzing time or an analyzing cycle, regardless of the analyzing time or the analyzing cycle.
In the single plunger type pump, since the liquid is delivered through repetition of the discharging operation and the quick sucking operation of the plunger, a pulsating flow is generated every cycle of the plunger reciprocating movement. In the double plunger type pump, also, the pulsating flow is generated due to shifting of the discharging operation and sucking operation of the two plungers in both parallel-type and a series-type.
Also, as an example of the liquid chromatography, there has been known a micro liquid chromatography for analyzing at a low flow rate in the order of, for example, 1-5 micro-liters/minute, by micrifying a separation column and a flow line. The micro liquid chromatography can be sensitized by suppressing diffusion of a sample, and allows the performance of the liquid chromatograph/mass spectrometer requiring carburation of the mobile phase containing separation components, to be maximized.
The pulsating flow appears as a noise of a detector base line, which may cause a bad influence in analyzing the results. Especially, in the micro liquid chromatography where the analysis is carried out at a low flow rate, the bad influence to the analyzing results by the pulsating flow is large.
The present invention has been made to solve the above problems, and an object of the invention is to provide a liquid chromatograph, wherein in case the liquid chromatograph is applied to the micro liquid chromatography, the influence of the pulsating flow to the analyzing result is suppressed.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A liquid chromatograph of the invention is basically formed of a liquid delivery mechanism having a pump with a plunger for delivering a liquid or mobile phase through a reciprocating movement of the plunger, a storing portion for storing each predetermined analyzing time and analyzing flow rate set beforehand, an operation portion electrically connected to the storing portion for calculating a liquid delivery quantity per analysis for an analysis to be performed or next analysis based on the analyzing time and the analyzing flow rate for the next analysis, a comparison portion electrically connected to the operation portion for comparing a pump capacity and the liquid delivery quantity for the next analysis, and a control portion electrically connected to the comparison portion and the liquid delivery mechanism for controlling a liquid transfer operation by the liquid delivery mechanism. When the comparison portion determines that the pump capacity is larger than the liquid delivery quantity for the next analysis, the control portion controls the liquid delivery mechanism to perform a low-flow rate liquid delivery mode where the liquid is delivered by only one cycle discharging operation of the pump during the analysis to be performed. Accordingly, influence by a pulsation flow from the pump is avoided in the analysis.